The present invention relates to an object sensing device for motor vehicles, and, more particularly, to a device having a transmitter/receiver pair for a reflex signal formed by an object situated in the driving direction, having a first operating mode for clear visibility and a second operating mode for poor visibility.
Known object sensing devices have the purpose of sensing obstacles in front of the motor vehicle and, if necessary, triggering the necessary measures. This includes the indicating of an imminent collision as well as, for example, an automatic brake intervention by way of which the motor vehicle is stopped in time. Corresponding devices are known, for example, from the applicant's German Patent DE-OS 37 01 340.
Although known devices offer a maximum of comfort because it is not necessary for the vehicle user to intervene in any way, a problem arises in that the emission of a signal as a result of a sensed obstacle takes place too frequently. The reason is that the vehicle user's potential for recognizing an obstacle and avoiding a collision is not taken into account sufficiently.
Swiss Patent CH-A-486702 shows a device in which the two operating modes are carried out by a varying amplification control of the receiver as a function of the respective visual range. Thus, compensation can be made for the effects of atmospheric or meteorological obstacles, such as layers of haze, rain clouds or snow clouds.
German Patent DE-A 32 22 263 shows a distance warning system for motor vehicles in which a radar system has a plain and a selective monitoring mode. The plain mode is present during straight-ahead driving at a relatively high speed, for example, on a turnpike; the selective monitoring mode is present in complex street traffic, that is, typically in city traffic. In the plain monitoring mode, on one hand, all vehicles are detected which drive ahead at the same speed or more slowly and which are standing and which come toward the vehicle. During the selective monitoring mode, on the other hand, only vehicles are taken into account which drive ahead at the same speed or at a slower speed.
The present invention has an objective of providing an object sensing device for motor vehicles which points out a threatening obstacle only if it is actually necessary.
The foregoing object has been achieved in accordance with the present invention by providing a signal emission for a first operating mode in the case of clear visibility for an object that is standing or is driving more slowly in the direction of motion of the motor vehicle, but not for an object which comes toward the motor vehicle, and for a second operating mode in the event of poor visibility, a signal emission also for an object coming toward the motor vehicle.
The present invention recognizes a distinction between different possible visibility conditions. In the case of operating mode I, clear visibility is assumed. In this mode, the vehicle user, as a rule, has the comprehensive potential of recognizing an obstacle in the form of standing or moving objects and of himself taking the corresponding measures for avoiding a collision. A signal is emitted only in a case in which he is overlooking an object which stands in front of him or moves in front of him at a reduced speed.
In the second operating mode II of the device, it is assumed that the visibility is poor. The vehicle user's perception is severely limited. Virtually every object that is sensed by the device represents a danger and must be signalled to the vehicle user.
Frequently, object sensing devices have a relatively large range. For the operating mode II, this means that relatively many, possibly even unnecessarily many object are sensed and a signal is emitted frequently. This can be prevented if the distance range can be selected within which an object is taken into account. The possibility exists in this case to adjust the distance range manually. This results in the advantage that the vehicle user receives responsibility and is caused to select his driving method consciously corresponding to the adjusted distance.
However, it is also possible to select the distance range automatically, for example, as a function of the vehicle speed. This may take place, for example, by means of an adjustment of the distance range (in meters) corresponding to half the vehicle speed (in km/h).
For mode I, it is assumed that relatively small obstacles, for example, objects on the side of the road, such as warning markers, parked vehicles, developments, etc., are, as a rule, recognized by the vehicle user himself, and he will control his vehicle correspondingly. Only actually critical objects are signalled which the vehicle user should perceive but does not notice at the moment because of a distraction or the like.
In order to better meet this requirement, also in the case of mode I, those objects are critically evaluated whose relative speed is equal to the vehicle speed and which are present continuously or always in the case of successive measuring operations. This applies in the case of an object standing in front of the motor vehicle, such as another motor vehicle or a wall.
Corresponding to an improvement of the invention, the device must also sense objects which move toward the motor vehicle and which have a specific size; this may, for example, be an obstacle which stands in the road. In this case, the process provides the use of two transmitter/receiver pairs which are aligned with scanning areas connected with one another. An object will be classified as being critical when both pairs receive a reflex signal from the same distance. As a result, smaller obstacles can easily be blanked out. They are recorded by only one transmitter/receiver pair.